Conventional facsimile machines capable of communicating color image information send and receive color image information in Lab color space, which has been determined by ITU-T Recommendations T.30, T.4, T.81 and T.42. With conventional color facsimile machines of this kind, no particular problems arise because they have been used to send and receive color documents. In recent years, however, digital still cameras have become quite popular and there is now increasing demand for the ability to transmit color image information, which has been captured by such a digital still camera, using the facsimile communication protocol as is. However, the color space of color image information used in such a digital still camera is sYCC color space and not Lab color space. In addition, digital cameras employ JPEG encoding as the method of encoding color images. In order to transmit an image captured by a digital camera, therefore, a protocol for transmitting JPEG code in sYCC color space as is has been studied.
In a case where image information captured by a digital still camera is transmitted, consideration has been given to the transmission, as is, of image files that have been stored on a memory card of the camera. For example, consider JPEG full-color transmission in sYCC color space. Basically, the object of transmission in this case often is not color document information but file information concerning images captured by a digital still camera and stored on a Compact Flash (registered trademark) card. Accordingly, for color document information, transmission in Lab color space has been considered. On the other hand, for file information acquired by a digital still camera or the like and stored on a Compact Flash (registered trademark) card, transmission in sYCC color space has been considered.
Accordingly, in a case where a JPEG-encoded file in sYCC color space has been received by an apparatus on the receiving side, no problems arise in regard to storing this file information on a Compact Flash (registered trademark) card. However, when an attempt is made to print the image on a print medium, it is necessary to decode the image file first and then print the image.
If in this case only the number of pixels in the JPEG-encoded file, and not the resolution and print size of the image, is specified by the apparatus on the transmitting side, how printing should actually be performed will be indefinite. Accordingly, the facsimile machine on the transmitting side transmits the resolution at which photography was performed by the digital still camera, without setting a resolution such as 200 dpi, unlike the case where ordinary color image data is transmitted. Consequently, when the facsimile machine that has received this image file decodes the image file and prints the decoded image on plain paper, a high-quality image will not be obtained.